Hurricane Sean (Mario's version)
Hurricane Sean was the most intense Atlantic hurricane to form in the month of December on record, and the first to exist in the respective month since Hurricane Epsilon in December of 2005. One of a few known systems to exist in the Caribbean Sea in the month of December, Sean was the eighteenth and final named storm as well as the eleventh hurricane of the hyperactive 2017 Atlantic hurricane season. The origins of Sean were first identified as a broad area of low pressure in the southwestern Caribbean Sea on December 4. Despite being in the off-season, unusually favorable conditions allowed development of the disturbance, before developing into a tropical depression on December 8, and a tropical storm shortly afterwards. Moving northeast, Sean slowly intensified, before becoming a hurricane on December 11. Increasingly unfavorable wind shear and dry air began to disrupt the hurricane shortly after peak intensity, and Sean made landfall very late on December 12 as a minimal hurricane in the eastern part of the Dominican Republic. Afterwards, rapid weakening ensued as it quickly accelerated into the subtropical Atlantic, before being absorbed by a cold front on December 14. Sean caused major destruction across its journey, killing a total of 434 people, making it the second-deadliest hurricane of the season, and caused $2.12 billion (2017 USD) in damages, mostly in the Dominican Republic and Puerto Rico , the latter of which was still recovering from the catastrophic destruction caused by Hurricane Maria only about three months earlier. Meteorological history Several days after the initial end of the infamous 2017 hurricane season, showers and thunderstorms persisted in the southwestern Caribbean Sea. The National Hurricane Center (NHC) began monitoring this area of disturbed weather in a Special Tropical Weather Outlook (STWO) issued on December 4 at 14:00 UTC for possible development. Unusually favorable conditions for the time of year allowed organization of the disturbance as it drifted sporadically within the southwestern Caribbean. Initially, it failed to organise significantly due to light to moderate wind shear. By December 6, the disturbance was assessed as having a high chance of tropical cyclogenesis as diffused banding features developed, however it was unclear whether a well-defined circulation existed. As it moved eastwards, the NHC initiated advisories on Potential Tropical Cyclone Twenty at 15:00 UTC on December 7 while it was located approximately 120 miles (280 km) north of Panama. The circulation became better defined overnight as it drifted northwards, and after an Air Force reconnaissance aircraft invenstigated the system the next day and found a well-defined circulation, the disturbance was upgraded to a tropical depression at 15:00 UTC on December 8. The nascent depression continued moving east-northeast in response to a mid-latitude trough that was over the southeastern Gulf of Mexico, and gradually intensified, ultimately become a tropical storm on December 9, and was assigned the name Sean – the first time a named storm existed in the Atlantic during the month of December since Tropical Storm Olga in 2007, and only the sixth time the "S" name was used for a storm in the Atlantic on record. With unusually warm sea surface temperatures of 84 °F (29 °C), strengthening was anticipated, with the only inhibiting factor being some dry air in the proximity of the storm, as well as low to moderate wind shear. By the next day, microwave and visible satellite images revealed that Sean had developed a mid-level eye along with a partial eyewall, with NHC forecaster Stacy Stewart stating "it is isn't out of the question that Sean becomes a hurricane if this rate of organization keeps up." Indeed, at 09:00 UTC on December 11, after reconnaissance aircraft found surface winds of 76 mph (127 km/h) and a diffuse eye, Sean was upgraded to a Category 1 hurricane, making it the first December hurricane since Hurricane Epsilon in 2005, and the first to form solely within the month since Hurricane Lili in 1984. The hurricane then turned to the northeast towards Hispaniola as the trough was replaced by a cold front to its northwest. A combination of observations including a ragged eye and a closed eyewall indicated that Sean attained its peak intensity at 03:00 UTC on December 12 with winds of 100 mph (155 km/h) and a central pressure of 976 mbar (28.7 inHg) while located about 200 miles (320 km) south of Hispaniola; this made it the most intense December Atlantic hurricane on record. Shortly afterwards, the proximity to land and the impending cold front began to take their toll on Sean as it neared the eastern tip of the island, with the eye clouding up and the eyewall fragmenting. At 22:30 UTC on December 12, Sean made landfall near the town of San Pedro De Macorís, Dominican Republic as a minimal hurricane – the first one to make landfall there since Hurricane Georges in 1998. After landfall, the rate of weakening accelerated as Sean crossed the peninsula, weakening to tropical storm status early on December 13, three hours after landfall, with the circulation becoming increasingly elongated. After quickly exiting into the extreme southern part of the subtropical Atlantic Ocean, Sean was ultimately declared post-tropical at 21:00 UTC later that day after the circulation became embedded within the cold front. The remnants of Sean dissipated roughly a day later. Preparations and impact Columbia Immediately upon the classification of the disturbance as a potential tropical cyclone on December 7, a tropical storm warning was issued for the northern coast of Columbia. Initially, the system was expected to track more eastwards and move very close to or make landfall in the country, which would've been a first in record keeping. Several flights were cancelled and schools were closed in advance of the storm. Projected rainfall amounts were expected to exceed 4 inches, with up to isolated amounts of up to 8 inches of rain in local areas. Despite Sean moving somewhat more northwards then expected, several areas recorded heavy rainfall, with the maximum amount of 6.56 in (16.66 cm) just northwest of Santa Marta. Flash flooding also occurred, which resulted in 5 deaths, and displaced around 150 people. Dominican Republic A hurricane watch was issued for the entire southern coast of the Dominican Republic on December 10 as Sean intensified to near hurricane intensity. It was later changed to a warning shortly afterwards. Despite being a category 1 hurricane, the NHC stressed the importance of not underestimating the impacts, as rainfall amounts were predicted to be as high as 15 inches with isolated amounts of potentially up to 20 inches. The potential of power outages were also likely as hurricane-force winds or gusts were expected to occur, especially closer to the eye of the storm. Schools were shut down and many flights were either redirected or cancelled due to the impending storm. The President of the nation, Danilo Medina, advised the residents to "hunker down and prepare for the worst". As Sean came ashore, very heavy rainfall in the rainbands associated with the storm triggered flash flooding and high winds gusts were reported. The highest wind gust that occurred during the storm was 107 mph (172 km/h), observed east of Santo Domingo, the nation's capital. Sean caused 133 fatalities in the Dominican Republic mainly due to flash flooding, although 3 people were killed beforehand when preparing for the storm; the exact cause of the deaths were not stated, but were said to have been indirectly related to Sean. Haiti Puerto Rico Still recovering from the catastrophic impacts of Hurricane Maria earlier in the season, many residents of the island were still without power and water had not been fully purified in much of the area. Aftermath See also *Tropical Storm Odette (2003) – another December storm in the Caribbean Sea which took an identical track *List of off-season Atlantic hurricanes Category:Predictions Category:Future storms